Sparkplug and process of manufacturing the same



Feb 27, 1968 H. J. BEARDSLEE, JR 3,370,331

SPARKPLUG AND PROCESS OF MANUFACTURING THE SAME Filed April 1, 1963 ATTORNEYS United States Patent O Ghia Filed Apr. 1, 1963, Ser. No. 269,270 Claims. '(Cl. 29--25.12)

The inventionA relates to sparkplugs and more particularly to resistor sparkplugs. n

In the present state of the art with respect to resistor sparkplugs, the resistor, while within the ceramicinsulator, is nevertheless subjected to environmental' conditions surrounding the sparkplug. It has therefore beenthe practice to protect the resistor from the effects of 'the environment with some electrically inert material.` Inspiteofsruch protection the surface coating can eventually break down, thus changing the resistorrvalue or allowing the ignition voltage to flash over the outside of the resistor body.

One of the objects of the present vinvention is to devise a method whereby the resistor Vcan be completely sealed within the sparkplug Vcavity thereby preventingconditions outside of the sparkplug from effecting any change in the resistor.

Another object is to provide a sparkplug construction having many advantageousfeatures, including not only a completely sealed resistorbut also good electrical conductivity between said resistor and the electrical conducting elements at the opposite ends thereof,

With these and other objects in view, the invention consists in the construction as hereinafter vset forth.

In the accompanyingdrawings: v

FIGUREI is a longitudinal section of a sparkplug insulator showing the relationship of the parts prior to the sealing operation. p

FIGURE 2 is a similar view of a complete sparkplug showing the final relationship of the parts after the seal has been accomplished.

As shown in the drawings, the ceramic insulator A, usually made of alumina, has an axial channel therethrough. This channel includes a small diameter portion B extending from the inner end to centrally within lthe insulator, a larger diameter chamber C extending toward the outer end, and an enlargement D at the extreme outer end. E is the center electrode having a head F seated on the shoulder at the bottom of the central chamber C. G is the resistor within the chamberC and H is the stud having a portion I for fitting the4 enlargement D and a flange l for seating on the top K of the insulator. The stud H has a depending portion L of reduced diameters, the lower end of which is threaded at M. According to the present invention the sparkplug has permanent` seals at both ends of the resistor and as indicated in FIGURE 2, N is the lower seal and O is the upper seal.

One method of manufacturing Vthe sealed'sparkplug of FIGURE 2 is illustrated in FIGURE l. The electrode E is inserted from the top of the insulator to extend through the bore B with the head F seated at the bottom of the central chamber C. The electrodeis made of nickel, nickel alloy such as Inconel, or other material which is both electrically conductive and capable of withstanding the combustion temperature and the products lof combustion to which the electrode will'be subjected in service. Above the head F, there Aisplaced a rlayer ,ofsealing material N the volume of which is larger than the'fnalseal N to allow for the shrinkage in size during vitrilication. Next, the resistor G is inserted from the top into the chamber C to rest on the layer N. Above the resistor there is placed a layer O of sealing material of larger volume than the final seal O to allow for shrinkage. Because of the large ICC initial volume of the sealing material, the upper layer of material O extends into or adjacent the enlargement D. Therefore the flange J of the stud |H is considerably above the top 'of the insulator before the sealing operation as shown in FIGURE 1.

To prevent any possibility of the material in the upper layer 'O' entering into any minute space surrounding the resistor G, it is necessary that the resistor should cornpletely fill the cavity. Therefore the resistor must be circumferentially coated with an electrically inert material P that will insure that there will be no unfilled space within the vchamber C.

After the assembly of the parts as thus far described. the structure is subjected to a vitrication and sealing process. The assembly is'raised to an elevated temperature which softens the material in layers N and O and then pressure is'applied to the stud H, compressing the entire asembly,'and forcing'the stud into the insulator until lthe ange I rests upon the end K of the insulator.

By reason of the temperaturey and pressure, the layers N and O'are vitrified and compacted into the shapes illustrated at N and O in FIGURE 2. This forms an effective seal at both ends of the resistor and places the resistor under invariable conditions which are independent of environmental conditions on the outside of the sparkplug.

In FIGURE 2 the sparkplug insulator is shown after the seals have been vitritied. It will be noted that the seals N and O are considerably smaller after vitrication than the original layers N and O. It will also be observed that the depending portion L of the stud H is embedded in the upper seal O with the threads M extending into the seal. There is no conductive sealing material surrounding the resistor G, due to the fact that the inert coating material P prevented any conductive material in layers O and N from flowing around the resistor during the sealing process. This inert material P moved axially with the resistor G when the pressure was applied during the sealing process and assisted in transmittingthe pressure to the lower layer of sealing material N to produce the final gas tight seal N. As shown in FIGURE 2, the resistor G is encapsulated between the two glass seals O and N and therefore the resistor is completely protected from the outside atmosphere by these two seals andthe ceramic insulator.

An important feature of the invention is the provision of theelectrically inert material surrounding the periphery of the electrical resistor. Without such coating it might be possible for'the conductive material in the layers O and N to enter into the space surrounding the resistor to a suflicient extent to impair the electrical effectiveness of the resistor. Accordingly an important feature of the invention is to provide suitable electrically inert material in the circumferential coating. The coating must be inert to temperature and electrical conductivity. A suitable material for this purpose is alumina, clay or talc powder or any combination of these materials with a suitable inorganic binder such as sodium silicate. The coating may be applied in various ways. It may be applied to the circumference of the resistor before inserting the resistor into the bore of the ceramic. It may be applied to the walls of the chamber C before placing the resistor into the cavity. The coating material may be applied afterv the resistor has been placed in the cavity and Vibrated or Apressed into a solid inert sleeve around the resistor.

The resistor coating can be varied somewhat depending upon which of the several methods aforementioned are used in applying it. If the coating is to be applied in the form of powder after the resistor has been inserted in the cavity, then plain talc or alumina or any other equivalent material inert to temperature and electrical conductivity can be used. The powderis vibrated and pressed around the resistor in the cavity to completely fill all small spaces. If the coating is applied before the resistor is inserted into thel insulator, then the coating material is preferably carried in some sort of vehicle. It can then be applied by spraying, dipping or by means of a roller or by extrusion. If the coating isto be applied to the resistor as a spray or dip or by means of a roller, then a suitable composition'for the purpose is talc and alumina in about equal amounts together with about 5% sodium silicate to act as a-bindcr and enough water to make the mixture of a consistency to be readily workable for whichever method of application is used. Where the coating material is to be applied by extrusion then it is preferable to use a composition containing about 5% clay, 2% sodium silicate and the remainder of talc or alumina or a combination of the two with enough water to provide a consistency suitable for extrusion. It is to be understood that the specific compositions above mentioned can readily be modified by the substitution of Ymaterials which are obvious equivalents thereto.

In carrying out the method as hereinbefore described, it is necessary that the layers N and O' shall be composed of a material which is electrically conductive and is susceptible of being vitrified. Such materials are known in the art and can be either a conductive cement type of seal, or a conductive glass seal. Also the material can be a non-conductive glass seal with a structural conductor extending through the same, such as a wire or spring embedded in the material.

The invention herein described is susceptible of various modications. For example, the upper and lower seals instead of being composed of electrically conductive material can be made of a non-conductive material and contact with the resistor can be made by means of a wire or by means of a spring. Another modification consists in using for the sealing material a conductive dry cement of the type disclosed in my Patent No. 2,798,980. When using such a material the lower seal is first'compacted in place, then the resistor with its surrounding inert coating is placed in the insulator bore and finally the upper seal is compacted into place. Another modification consists in using for the upper and lower seals a self-hardening cement material so that the resistor is icontained between upper and lower cement seals and is thereby protected from environmental conditions outside of the sparkplug.

With the invention as above described, I have provided a novel sparkplug construction in which a resistor is secured in the ceramic insulator between two seals. The method of construction is such as to readily permit the resistor to be placed in a cavity within the insulator and then sealed into place.

The novel construction prevents shorting out the resistor either to the cavity or across the terminal ends. It provides a completely encapsulated resistor that cannot come into contact with the outside atmosphere or humidity. The assembly becomes virtually non-destructive when operated within the limits of design.

The improved sparkplug of this invention has the ability of improving the characteristics of the resistor by means of increasing its current rating because heat canV easily be dissipated into the surrounding materials. The sparkplug has a longer life'due to the increased current rating of the resistor constructed and arranged in the manner set forth herein. By reason of the intimate contact between resistor and ceramic walls, the resistor is enabled to dissipate more heat load into the ceramic body. The encapsulated, hermetically sealed condition produced by reason of this invention improves the resistorgvoltage characteristics by insulating completely -arund'tlie resistor and thereby preventing ashover.

What l claim as my invention is: y

The method o f making a resistorfs'parkplug comprising inserting an electrode in one end of an insulator -to extend into the longitudinal central hollow portion within said insulator in contact with said resistor, insert-V ing a plug within said insulator into contact `with' said second layer and subjecting said plug, said layers of conductive material and said coated resistor to endwise pressure while heating to vitriiication temperature to thereby compact said conductive layers, vitrify the same and form permanent seals between the opposite ends of said resistor while preventing access of conductive material into said space surrounding said resistor.

2. The method according to claim 1 wherein after the insertion of said first layer of conductive vitrifiablermaterial and said resistor into said insulator a non-conductive powdered material is tamped into the space around said resistor to completely fill said space to the top of said resistor and thereby prevent subsequent penetration by said vitriable material from the first and second layers aforesaid.

3. In a method of making a resistor sparkplug having a resistor within a ceramic insulator and having a pair of conductive vitreous seals at opposite ends of said resistor adjacent an electrode and a conductor respectively, the improvement which consists in first protecting the resistor by impregnating the outer surface with a nonconducting coating to increase the diameter thereof to such an extent that it completely fills the cavity in said ceramic insulator, andv then subjecting said seals and coated resistor to endwise pressure while heating to vitrification temperature to thereby compact and vitrify said seals, said coating which completely fills the cavity preventing the entry of any vitrifiable material between the resistor and the ceramic body.

4. The method of making a resistor sparkplug cornprising inserting an electrode in one end of an insulator to extend into the longitudinal central hollow portion thereof, applying a layerV of conductive vitrifiable material within said insulator in contact with said electrode, inserting a preformed resistor into said central portion to contact with said layer, providing a non-conductive coating in said central hollow.portionfsurrounding said resistor above said layer of conductive vitrifiable material to such an extent that it completelyV fills the space surrounding said resistor to the level of the top of said resistor, applying aV second Vlayer of conductive vitrifiable material within said insulator in contact with said resistor, inserting a plug within said insulator into contact with said second layer andv subjecting saidplug, said layers of conductive material and said coated resistor to Veudwise pressure while heating to vitrication temperature tosthereby compact said conductive layers, vitrify the same and form permanent seals between the opposite ends of said resistor while preventing access of conductive. material into said space surrounding said resistor,said resistor prior to insertion being provided with said nonconductive coating to such an extent that it fits clsely into the central hollow portion surrounding said resistor and prevents access into said space of said conductive vitrifable material during the application of heat and pressure. n

5. The method according to claim 4 wherein the'preformed resistor prior to insertion into said central hollow portion is coated with a composition comprising alumina and talc bonded with sodium silicate.

(References onv following page) References Cited UNITED STATES PATENTS Cipriani et al 315-58 Dressel 315-58 Stuermer 29--25.12

`Candelise 29-25.12 Rabezzana 315-58 X 6 2,453,048 11/ 1948 Tognolla 3 15-5 8 2,459,282 1/1949 McDougal 315-58 2,717,43 8 9/ 1955 Schwartzenwalder 29-25.12

5 WILLIAM I. BROOKS, Primary Examiner.

ROBERT SEGAL, I OHN F. CAMPBELL, CHARLIE T.

MOON, Examiners.

D. E. SRAGOW, Assistant Examiner. 

3. IN A METHOD OF MAKING A RESISTOR SPARKPLUG HAVING A RESISTOR WITHIN A CARAMIC INSULATOR AND HAVING A PAIR OF CONDUCTIVE VITREOUS SEALS AT OPPOSITE ENDS OF SAID RESISTOR ADJACENT AN ELECTRODE AND A CONDUCTOR RESPECTIVELY, THE IMPROVEMENT WHICH CONSISTS IN FIRST PROTECTING THE RESISTOR BY IMPREGNATING THE OUTER SURFACE WITH A NONCONDUCTING COATING TO INCREASE THE DIAMETER THEREOF TO SUCH AN EXTENT THAT IT COMPLETELY FILLS THE CAVITY IN SAID CERAMIC INSULATOR, AND THEN SUBJECTING SAID SEALS AND COATED RESISTOR TO ENDWISE PRESSURE WHILE HEATING TO VITRIFICATION TEMPERATURE TO THEREBY COMPACT AND VITRIFY SAID 